This invention relates to a process for the extraction of aromatics from mixed aliphatic/aromatic hydrocarbon feeds such as isomerization process feed streams, cat naphthas, lube stocks, and the like. More particularly, this invention is concerned with the use of liquid salts, in particular, quaternary ammonium, phosphonium and arsonium salts of halides, acids, or more complex anions, as extracting agents for aromatics from paraffin feedstreams. Such salts show the required solubilities in various solvents and low volatility to allow for a distinct selectivity advantage over more conventional solvents, particularly sulfolane, which is commercially used. Such salts also show the exceptionally low volatilities typical of salts, thus minimizing losses by vaporization and facilitating recovery of extractate.
In certain instances, aromatics in hydrocarbon feedstreams can act as catalyst poisons such as in isomerization feedstreams. Then, the aromatics must be removed prior to the paraffin isomerization reaction. In this instance, sulfolane cannot be used since it is partially miscible with the paraffinic hydrocarbon and would also tend to poison the isomerization catalyst. By contrast, liquid salts which have a high affinity for aromatic hydrocarbons and are insoluble in the paraffinic hydrocarbon/carrier, are excellent extractants since they are readily separated from the paraffinic hydrocarbon feedstream and pose no catalyst poisoning hazard.
Specific objects of this invention are to provide a process utilizing liquid salts, having a high extractive selectivity for aromatic compounds and high solvation capacity, are readily synthesized from low cost, readily available materials, and can easily be stripped or separated from the extraction phase, and which have high thermal and chemical stability.